[Elecraft] SDR Technology

[Geoffrey Feldman]

Hi Walter,

In response to your comments on my post, the terminology you use and that I
used both appear in various texts to describe the same thing. Not
surprising, we both know what one another mean.  I prefer incident because
quadrature is in relationship to that.  An AM signal would appear on the
incident stream.  Quadrature then is necessary for most (all) of the other
modulation schemes.  In software the in-phase or incident stream appears as
the real part of the complex number. That fits with the idea of incident for
me.  Tomato tomatoe.    

 

Actually I meant direct conversion.  I was referring broadly to SDR but
thinking of the KX3 which I own and not the K4 which I am less familiar
with.  I'll have to look at the K4 more carefully but it sounds like its
architecture is what I called Hybrid.  That would make sense given its price
point and less portable size along with better performance.  Would you then
consider the Yaesu FTDX-101D as more similar to your understanding of the K4
architecture (excepting the yaesu rather goofy interface, in my personal
opinion). I expect it's not exactly the same but how would you compare them
from an SDR perspective?  Getting from RF to base band and back to RF is
relatively straight forward. The interesting stuff IMHO is Fast Fourier,
Filters and other fun software stuff.

 

In responding to a list serve, we are writing off the cuff.  If one
understands the other and then has useful discussion, it's good for me.  I
will look over the books I have and review using whatever the more common
and clear terminology is.  I'm by no means an expert and I am learning
myself.  My primary interest is in system architectures.  My interests go
beyond Elecraft. I seek a taxonomy of SDR implementations which might be
helpful in comparing products or understanding innovations.

 

Thanks for the link. I was aware of that among other sources.  Here is one
that I have found helpful: Practical Signal Processing by Mark Owen.  I am
sure you know this link: https://greatscottgadgets.com/sdr/ He mentions
Owen's book as well.  This is also quite good with a discussion of the
Tayloe mixer/detector (again two used terms).
https://www.arrl.org/files/file/Technology/tis/info/pdf/020708qex013.pdf
Here is a discussion of Tayloe that I think is helpful
http://www.norcalqrp.org/files/Tayloe_mixer_x3a.pdf   As for history, if you
look at John Renshaw Carson's original paper on SSB you will see the
concepts of IQ in his calculus.  Here is Wikipedia.
https://en.wikipedia.org/wiki/Single-sideband_modulation   Fun fact, there
is a picture of Einstein, Sarnoff, Steinmetz and others with someone often
falsely claimed to be Tesla. It isn't. It's Carson.

 

Geoff 

W1GCF